I'm on the side of the square TE's, it causes the disruptive airflow to occur farther past the TE than a rounded one will. I heard a rumor once that if flag poles were square the flag wouldn't ripple in the wind. If you can find Ed Mormons web page, he has some really good info on this subject of TE's. If anything, I would taper it to a sharp point if it were a faster plane, but leave them square for a fun-fly type plane.